1. The Field of the Invention
The present invention relates to the field of orthodontic brackets. Such brackets comprise a fiber and/or particle-reinforced polymer material.
2. The Relevant Technology
Orthodontics is a specialized field of dentistry that involves the application of mechanical forces to urge poorly positioned, or crooked, teeth into correct alignment and orientation. Orthodontic procedures can be used for cosmetic enhancement of teeth, as well as medically necessary movement of teeth to correct underbites or overbites. For example, orthodontic treatment can improve the patient's occlusion, or enhanced spatial matching of corresponding teeth.
The most common form of orthodontic treatment involves the use of orthodontic brackets and wires, which together are commonly referred to as “braces.” Orthodontic brackets, more particularly the orthodontic bases, are small slotted bodies configured for direct attachment to the patient's teeth or, alternatively, for attachment to bands which are, in turn, cemented or otherwise secured around the teeth. Once the brackets are affixed to the patient's teeth, such as by means of glue or cement, a curved arch wire is inserted into the slot of each bracket. The arch wire acts as a template or track to guide movement of the teeth into proper alignment.
There are two distinct classes of orthodontic brackets: those that require the use of ligatures to fasten the arch wire to the bracket, and those that are self-ligating. In brackets of the first type, small ligature wires or elastic bands are typically used to hold the arch wire in a securely seated position in the brackets. Ligatures or some other form of fastening means are essential to ensure that the tensioned arch wire is properly positioned around the dental arch, and to prevent the wire from being dislodged from the bracket slots during chewing of food, brushing of teeth, or application of other forces. One type of commercially available ligature is a small, elastomeric O-ring, which is installed by stretching the O-ring around small wings known as “tie wings” that are connected to the bracket body. Metal ligatures are also used to retain arch wires within the bracket slots.
In an effort to simplify the process of installing braces, a variety of self-ligating brackets have been developed. The term “self-ligating bracket” refers to a class of orthodontic brackets that include some sort of cover, whether separate from or hingedly or slidably attached to the base, which encloses or otherwise retains the arch wire within the slot of the base. Examples of self-ligating brackets are disclosed in U.S. Pat. Nos. 3,748,740, 4,077,126, 5,857,849, and 6,071,118.
Self-ligating brackets have grown in popularity because of their convenient features, but they still exhibit certain disadvantages, not least of which is that they can be rather fragile if made from polymers. In addition, many polymers can deform (or “creep”) over time, especially when the constant force from an arch wire is applied thereto. Metal brackets are strong, but have the distinct disadvantage of being less attractive and providing sharp, jagged, or hard edges that can cause injury.
Therefore, there exists a need for materials that impart increased strength and durability to polymeric orthodontic brackets, whether self-ligating or non-self-ligating.